Improvements in Electric Lighting: Incandescent Lamps.
While the Welsbach mantles have been constantly improved in quality, and given new and inverted forms of special value, the inventors in the field of electric lighting have not stood still. For interior illumination the Edison incandescent bulb still holds its own despite many a threat of dispossession. Since 1881 its details of manufacture have been steadily bettered and its price much reduced, while its consumption of current has fallen from 5.8 watts per candle to 3.1. This advance, marked as it is, leaves a long path ahead of the inventor whose estimate is that were the whole of an electric current transformed into light, a candle would cost us but .11 of a watt, that is, but one twenty-eighth part as much as when we set a carbon filament aglow. In electrical terms a horse-power yields 748 watts, representing, were there no waste in conversion, no less than 425 lamps each of 16 candle-power.
Alcohol lamp with ventilating hood.
It is this immense margin for improvement that has spurred ingenuity to attack the problem of electric lighting from many new sides. The General Electric Company produces a carbon filament of one fifth greater efficiency than an ordinary untreated filament. Fibers of the usual cellulose kind are enclosed in a carbon box, placed in a carbon-tube resistance furnace heated to between 3,000° and 3,700° C. This converts the filament into a graphite of increased luminosity which, furthermore, blackens its enclosing glass much less than a common filament does.
Welsbach mantle.
In the early days of electric lighting a good many experiments were tried with threads of platinum, but without success. That metal remains unmelted at a very high temperature, but as a light-giver its quality is poor. Of late years investigators have turned to other metals, of high melting points, and with results so remarkable that we may expect some of them to be in general use in the near future. Tantalum, a rare and costly metal, has been found to give a candle-power with as little as two watts and, in specially favorable circumstances, with only 1.85 watts. Osmium, in the hands of Dr. Auer von Welsbach, reduces this figure to 1.5 watts. Dr. Hans Kuzel, of Baden, Austria, has employed filaments of tungsten in lamps which he claims demanded only one watt per candle. From among these new lamps it seems highly probable that as soon as methods of manufacture are settled and standardized the world will be given an electric light, in small units, much cheaper than ever before.
Tantalum lamp.